Discovery Signal Transmitted in Direct Communication System, and Method of Transmitting/Receiving the Discovery Signal

1. A method in which a first mobile device joining in device to device direct communication transmits a discovery signal, the method comprising: transmitting a first discovery signal for discovering a device using at least one of a plurality of discovery resources in one of a plurality of discovery frames for device or service discovery included in an ultraframe, each discovery frame including a plurality of discovery resources that belong to a same resource class of a plurality of resource classes, the plurality of resource classes being periodically available with different cycles, each of the cycles being no smaller than a cycle of the ultraframe; and transmitting a second discovery signal for discovering a service using the ultraframe, wherein the first and second discovery signals have a same format, and each include a first field representing whether the first discovery signal is a signal for discovering a device or a signal for discovering a service, and a second field comprising one of device identifier information (Device ID) of the first mobile device and service information of a service that the first mobile device provides according to a value of the first field, and a time interval between each of the plurality of discovery frames corresponds to a length of a plurality of superframes.

2. The method of claim 1 , wherein the second discovery signal is transmitted via the at least one discovery resource.

3. The method of claim 2 , wherein a position of the at least one discovery resource in each period is constant.

4. The method of claim 3 , wherein the transmitting of a first discovery signal comprises periodically broadcasting the first discovery signal N times using the at least one discovery resource, and the transmitting of a second discovery signal comprises periodically broadcasting the second discovery signal M times using the at least one discovery resource after the first discovery signal is broadcasted N times, N and M each being a natural number.

5. The method of claim 1 , wherein the at least one discovery resource is a resource of a determined position according to a hopping pattern.

6. The method of claim 5 , wherein the transmitting of a second discovery signal comprises periodically broadcasting the second discovery signal M times after the first discovery signal is periodically broadcasted N times, and N and M are each a natural number, and are varied.

7. The method of claim 1 , wherein the transmitting of a second discovery signal comprises: masking the service information using the Device ID; inserting the masked service information into the second field; and broadcasting the second discovery signal through a radio channel.

8. A method in which a first mobile device joining in direct communication receives a discovery signal, the method comprising: receiving the discovery signal transmitted via at least one of a plurality of discovery resources in one of a plurality of discovery frames for device or service discovery included in an ultraframe, each discovery frame including a plurality of discovery resources that belong to a same resource class of a plurality of resource classes, the plurality of resource classes being periodically available with different cycles, each of the cycles being no smaller than a cycle of the ultraframe; determining whether the discovery signal is a signal for discovering a device or a signal for discovering a service based on a value that is stored at a first field of the received discovery signal; acquiring, when the discovery signal is a signal for discovering a device, device identifier information (Device ID) that is stored at a second field of the discovery signal; and acquiring, when the discovery signal is a signal for discovering a service, service information that is stored at the second field of the discovery signal, wherein the discovery signal comprises: the first field representing whether the discovery signal is a signal for discovering a device or a signal for discovering a service; and the second field comprising one of the Device ID of a device that transmits the discovery signal and the service information of a service that a device that transmits the discovery signal provides according to a value of the first field, and a time interval between each of the plurality of discovery frames corresponds to a length of a plurality of superframes.

9. The method of claim 8 , further comprising unmasking the acquired service information using the acquired Device ID.

10. The method of claim 1 , wherein the service information comprises: service type information representing a type of the service; service identifier information of the service; service status information representing a providing status of the service; and time information that is related to the service status information.

11. The method of claim 10 , wherein the service type information represents one of unicast transmission, multicast transmission, and broadcast transmission.

12. The method of claim 10 , wherein the service status information represents one of a start status of the service, a continue status of the service, and an end status of the service, and the time information represents a start time of the service when the service status information represents the start status, and the time information represents an end time of the service when the service status information represents the end status.

13. The method of claim 1 , further setting a direct communication path on a radio channel after the service is discovered.

14. The method of claim 8 , further setting a direct communication path on a radio channel after the service is discovered.

15. The method of claim 1 , wherein at least one of the cycles of the resource classes is larger than the cycle of the ultraframe.

16. The method of claim 8 , wherein at least one of the cycles of the resource classes is larger than the cycle of the ultraframe.